The present invention relates to Fe-base soft magnetic alloy powder having excellent magnetic properties and applications thereof, and more particularly to Fe-base soft magnetic alloy powder having a low magnetostriction, and applications thereof as transformers, choke coils, saturable reactors, etc. and methods of producing them.
Conventionally, magnetic cores for transformers, motors, chokes, noise filters, etc. are made of crystalline materials such as Fe-Si alloys, Permalloy, ferrites, etc. Fe-Si alloys, however, have large specific resistance and their crystal magnetic anisotropy is not zero. Accordingly, they suffer from large core losses at a relatively high frequency. Permalloy also has a high core loss at a high frequency.
Conventionally used widely as magnetic powder materials for high-frequency transformers, saturable reactors, choke coils, etc. are mainly ferrites having such advantages as low eddy current loss.
However, despite the fact that ferrites have small core losses at a high frequency, their magnetic flux densities are at most 5000 G. Accordingly, when they are operated at a large magnetic flux density, they are close to saturation, leading to large core losses.
Recently, transformers operable at a high frequency, such as those for switching regulators are required to be miniaturized. For this purpose, the magnetic flux density in an operating region should be increased. Thus, the increase in a core loss of ferrites may become a serious problem for practical applications.
For the purpose of decreasing a core loss at a high frequency and improving frequency characteristics of permeability, dust cores of crystalline magnetic alloys are conventionally used. The dust cores are prepared by forming fine powder of the magnetic alloys and solidifying it via insulating layers. For such insulating layers, organic materials are used. Such magnetic dust cores are mainly used for chokes, noise filters, etc.
However, since the dust cores made of the conventional crystalline magnetic powder have small permeability, a large number of winding is necessary to achieve sufficient inductance, making it difficult to miniaturize magnetic cores constituted by such dust cores. In addition, since they have large core losses, a lot of heat is generated during their use.
Recently, as an alternative to such conventional magnetic materials, amorphous magnetic alloys having high saturation magnetic flux densities have teen attracting much attention.
These amorphous alloys are essentially composed of Fe, Co or Ni, etc. as a basic element, and at least one of P, C, B, Si, Al, Ge, etc. as a metalloid which can make the resulting alloys amorphous. Further, it is known that there are amorphous alloys composed of Fe, Co or Ni and Ti, Zr, Hf, Nb, etc. without metalloids, which can be produced by a roll method.
However, since amorphous magnetic alloys are tough and difficult to be pulverized, they are generally produced in the form of a thin ribbon and the thin ribbon is laminated or wound to form a magnetic core.
To form a magnetic core from the thin ribbon, it should be formed into a toroidal wound core or cut into a desired shape such as a U-shape or an E-shape and then laminated. However, when a U-shape or E-shape magnetic core is desired, its production is generally difficult.
To eliminate this problem, various methods of producing dust cores by pulverizing an amorphous magnetic alloy and compressing the resulting powder together with a binder were proposed. See, for instance, Japanese Patent Laid-Open Nos. 55-133507, 61-154014, 61-154111, 61-166902, etc. Further, various methods of producing dust cores with high densities by instantaneously applying an impact force to amorphous magnetic alloy powder were proposed. See, for instance, Japanese Patent Laid-Open Nos. 61-288404 and 62-23905.
Amorphous alloys which may be used for such dust cores are mainly classified into two categories: iron-base alloys and cobalt-base alloys. Fe-base amorphous alloys are advantageous in that they are less expensive than Co-base amorphous alloys, but they generally have larger core loss and lower permeability at high frequency than the Co-base amorphous alloys. On the other hand, despite the fact that the Co-base amorphous alloys have small core loss and high permeability at high frequency, their core loss and permeability vary largely as the time passes, posing problems in practical use. Further, since they contain as a main component an expensive cobalt, they are inevitably disadvantageous in terms of cost.
In any case, alloy powder and dust cores having sufficiently high saturation magnetic flux density and other good magnetic properties cannot be obtained from Fe-base or Co-base amorphous alloys.